The time-honored method of isolating or removing particular positional isomers from isomeric mixtures of disubstituted aromatic compounds has been the classical fractional distillation technique. This method, however, has not been very practical on an industrial scale unless there is a significant difference in the boiling points of the various isomers. In terms of many important industrial aromatic compounds, particularly those having one or more polar substituents, separation or significant enrichment of particular isomers by boiling point is an extremely difficult and expensive endeavor, and at times is quite impossible. The table below will illustrate the problem with the boiling points of a few typical compounds.
______________________________________ B.P., .degree.C. Name ortho meta para ______________________________________ Hydroxy isopropyl benzene (isopropylphenol) (cumenol) 213-4.sup.a 228.sup.a 228-30.sup.b Amino isopropyl benzene (isopropylaniline) 220-1.sup.b 225.sup.a Chloro isopropyl benzene 191.sup.c 65.sup.7mm 198.3.sup.a (chlorocumene) 62-68.sup.8mm Methyl benzaldehyde (tolualdehyde) 200.sup.a 199.sup.a 204-5.sup.a Chlorobenzaldehyde 211.9.sup.a 213-4.sup.a 213-4.sup.a ______________________________________ .sup.a 760 mm Hg .sup.b 745 mm Hg .sup.c 745.6 mm Hg
U.S. Pat. No. 3,029,300 to Schaeffer discloses a selective clathration process for the separation of xylene isomers, but such a process involves an elaborate procedure requiring the employment of very specialized and expensive equipment.
A catalytic process for the selective production of particular xylene isomers, utilizing a platinum on alumina catalyst, is disclosed in U.S. Pat. No. 3,078,318 to Berger.
Selective production of para dialkylbenzenes in the presence of specific zeolite catalysts is described in U.S. Pat. Nos. 3,965,209 to Butter, et al.; 4,001,346 to Chu; 4,086,287 to Kaeding et al; and 4,090,981 to Rodewald.
While the above-noted prior art is considered of interest in connection with the subject matter of the present invention, the selective cracking process described herein utilizing the specified type of zeolitic catalyst to achieve selective removal of 1,4-disubstituted aromatic compounds having polar substituents from mixtures containing the 1,2 and 1,3 isomers of such compounds has not, insofar as is known, been heretofore disclosed.